A reverse osmosis (RO) system includes a membrane. When feed water enters the system, some water goes through the membrane as purified permeate and some is left as concentrate. When the system is shut off, there is no flow through the system and the salts and impurities can slowly diffuse through the membrane from the concentrate side into the permeate side. When the system is turned on again, this results in the delivery of permeate having a higher concentration of impurities being delivered to the faucet than when the system was turned off.